NOTE  ON  THE  CONUS  ARTERIOSUS  OF  MEGALOPS 
CYPRINOIDES  (BROUSSONET)  . 


H.  D.  SENIOR,  M.B.,  F.R.C.S. 


[Reprinted  from  Biological  Bulletin,  Vol.  XII.,  No.  6,  May,  1907.] 


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NOTE  ON  THE  CONUS  ARTERIOSUS  OF  MEGALOPS 
CYPRINOIDES  (BROUSSONET). 

H.  D.  SENIOR,  M.B.,  F.R.C.S.,  . 


Associate  in  Anatomy,  Wistar  Institute  of  Anatomy,  Philadelphia. 


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Since  describing  the  conus  arteriosus  in  Tarpon  Atlanticus 1 I 
have  been  fortunate  in  securing  a specimen  of  Magalops  cyprin - 
6 'ides.  For  this  I take  the  present  opportunity  of  thanking 
Professor  David  Starr  Jordan. 

The  fish  in  question,  preserved  in  alcohol,  measures  19  cm. 
(including  caudal  fin)  so  that  the  heart  is  extremely  small,  and  is, 
on  account  of  its  somewhat  friable  condition,  difficult  to  handle. 

The  conus  is  everywhere  quite  obvious  from  the  exterior.  Fig. 
1,  drawn  from  the  left  side,  indicates  that  the  general  form  of 


Fig.  i.  Fig.  2. 


Fig.  1.  Entire  heart  of  Megalops  cyprinoides  from  the  left  side,  X 3*  A small 
portion  of  the  atrium  has  been  removed  to  display  the  conus  more  fully. 

Fig.  2.  Frontal  section  through  the  right  side  of  the  heart  of  Me^alops  cypri- 
noides, showing  the  relations  in  the  conus  region,  X IO- 

conus  and  bulbus  resembles  that  of  Amia  rather  than  that  of 
Tarpon. 

The  heart  was  opened  by  a mid-ventral  sagittal  incision,  it  having 
been  previously  ascertained  that  such  an  incision  would  fall  be- 
tween the  valves  without  cutting  them.  After  examination  and 

1 Biol.  Bull.,  February,  1907,  p.  145.  (The  literature  on  the  conus  arteriosus 
is  given  in  this  article. ) 


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379 


H.  D.  SENIOR. 


measurement  the  two  halves  were  imbedded  in  celloidin  and  cut 
into  serial  sections. 

The  extreme  length  of  conus  is  I mm.  in  the  mid-ventral  line 
and  1.5  mm.  in  the  mid-dorsal  and  lateral  lines.  The  ventricle, 
from  apex  to  junction  with  conus,  has  a mean  measurement  of 
5.5  mm.  The  proportion  in  mean  length  of  conus  to  ventricle 
is  therefore  1 to  4. 

The  conus  contains  two  transverse  tiers  of  valves,  each  tier 
consisting  of  a right  and  left  cusp  placed  symmetrically  with  re- 
gard to  the  mid-sagittal  plane.  The  general  arrangement  agrees 
closely  with  that  found  in  Tarpon , but  the  proximal  cusps  appear 
to  be  proportionately  more  capacious. 

The  conus  in  Megalops  not  only  projects  more  freely  from  the 
ventricle  than  in  Tarpon,  but  is  of  greater  proportionate  length. 
It  would  seem  to  resemble  more  closely  the  conus  of  Albula  (as 
described  by  Boas,  ’8o)  except  in  the  absence  of  the  subsidiary 
valve  cusps  of  the  latter. 

It  should  be  noticed  that  the  heart  described  is  from  a young 
fish,  also  that  the  measurements  are,  at  best,  approximate  ; there- 
fore, comparisons  with  adults  of  other  genera,  if  pushed  too 
closely,  are  apt  to  be  misleading. 

The  atrio-ventricular  valve  has  three  cusps. 

A specimen  of  Chanos  chanos  (Forskal),  for  which  I also  have 
to  thank  Professor  Jordan,  presents  an  easily  recognizable  ves- 
tigial conus  arteriosus,  but  only  one  tier  of  valves. 

St.  Louis,  Mo.,  February  1,  1907. 


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